How to delete photos synced to my iPhone?

A week or so ago, I synced some pictures from my computer to my iPhone so I could email them to a friend. Now, I don't know how to get them off my phone. Help, please. :/

Added (1). Photos synced from iTunes can't be deleted like photos taken or saved.No, I'm not THAT technologically challenged.

Open the picture and then click the trash can.

Connect your iPhone to your pc then start iTunes and from there you can delete your sync photos

Connect your phone to the pc, open the iTunes software then click on the "Photos" tab. Check the selected photo folder on your computer and open the sync photo directory. Delete all the custom made photo folders on your computer then click on "Apply" button to start syncing your iPhone.